Particularly interested if anyone spots errors in capacitor and resistor values make sense as I modified the circuit from one found somewhere else without fully understanding it. :o
(The data sheet had every example except the simplest use case which happens to be the one I wanted! But most of it looks the same as here, so I am fairly confident).
Driving a 48V motor that wants 5A to run. Generally run for no more than 30 seconds at a time with minutes to hours between.
Added some extra capacitors and diodes (that appear to be for extra circuit safety) from the datasheet reference designs. Also the resistor and capacitor across the load appear to be of suitable value if I correctly understood the bit in the datasheet on how to calculate those.
I'm pretty confident here now but since I intend to release the finished and tested board design files public domain for anyone else who has a use for it, I want it to be the best reasonably possible, so any comments/suggestions are very welcome.
Oh, FYI, the project I am using this h-bridge for is here: Glenn's Bed
That chip cannot really handle 5A, that's the absolute max peak value (certainly not continuous).
You need a bridge with discrete MOSFETs to handle 5A. Perhaps look at the HIP4081A driver which
forms a bridge with 4 n-channel MOSFETs.
(The device on-board D-FETs are 0.3 ohm, ie 300 milliohm. For 5A you want 10 milliohm or
less ideally). 5A at 0.3 ohm is ~8W per switching device, ~15W total, which is massive.
And remember a motor with 5A normal load will have stall current of 30 to 60A, which will definitely explode that chip.
You have a problem, but don't know how to solve it, so tell us the problem, not your guesses at
how to solve it.
From what I can see you need to drive a couple of linear actuators - so tell us full details of this
hardware and your requirements for controlling them. Do you need speed control for instance?
Thanks for all the advice. I have settled on using PCB-mount 120VDC@10A relays (5v drive via BC547 and flyback diodes). Non-latching so the default state is all-off via GND-GND. (I have the circuit up on Glenn's Bed --near the bottom-- if anyone is interested)
For some applications, this could be a problem. Might be a problem in your application!
I suspect that the motor in those actuators is heavily geared down and will stop quickly without frying the relays. I would suggest testing out the 2 relay circuit on the motor to see if it works acceptably or if melts the relay contacts.
Thanks for the heads-up on that, Daenerys. I ordered relays rated over double my needs in V and A (DC ratings, not AC ) for normal operation, and according to their datasheet they can handle a 6kV surge, so If that doesn't do it I am not sure if anything will!
And yes, you are right that the motors stop very suddenly due to the gearing.
